On October 12, 2005, EPA promulgated final replacement standards for Phase I units and standards for Phase II units under the National Emissions Standards for Hazardous Air Pollutants from hazardous waste combustors (HWC MACT). Phase I units are incinerators, cement kilns, and lightweight aggregate kilns firing hazardous waste. Phase II units are solid fuel boilers, liquid fuel boilers, and hydrochloric acid production furnaces that fire hazardous waste. The EPA granted reconsideration on certain issues and revised standards were subsequently promulgated on October 28, 2008. The EPA subsequently received a voluntary remand of all standards August 14, 2009. This notice of proposed rulemaking, published on July 24, 2024, proposed to remove emission limit exemptions for periods of malfunction from the rule in keeping with the Sierra Club v. EPA, 551 F.3d 1019 (D.C. Cir. 2008) ruling and add e-reporting requirements to the rule. This action would provide for simplified reporting by owners and operators of hazardous waste combustors and enhance the availability of data to EPA and the public.